/**
 * Implement a basic calculator to evaluate a simple expression string.
 * The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, 
 * non-negative integers and empty spaces .
 * You may assume that the given expression is always valid.
 * Some examples:
 * 
 * "1 + 1" = 2
 * " 2-1 + 2 " = 3
 * "(1+(4+5+2)-3)+(6+8)" = 23
 */
/**
 * @author I321035
 *
 */
package problem224_Basic_Calculator;